Overall very pleasant.
This game just seems to succeed at what it sets out to do. For those just wanting to have something light and fun, it is possible to just breeze through levels, though you won't get three starts each time. And for those wanting more challenge, well, that's what the star system is for - I found it very fun to keep trying and trying to do each stage just right. I liked how each star was achieved in its own way, instead of just being "higher score = more stars" like with many games. Furthermore, the challenge levels are really quite interesting, especially for those of us who just can't get enough challenge in a game, adds a lot of replay value for the sake of getting each and every star available. The ability to come see the planet after completing levels was nice as well.
As for the mechanics, I enjoyed the physics that the game used, gravity, etc. It was fun getting the orbital achievement that way too. I can't really find much to even nitpick about this - the closest thing I can come up with was that it's a little frustrating trying to click in just the right place while the ship was already moving at a decent speed. But hey, more challenge that way, right?
Finally, I loved the music and the visuals. They weren't overly simple, nor overly detailed. They fit the game well, and to see that paired with such nice music to listen to while playing was a really nice experience. The music isn't dominating, either, so one can just play without being distracted by a barrage of sounds. I found myself keeping the music on even when I had to switch tabs to work on other things for a while. (I have to admit, autumn was my favorite.)
Overall, this was a really nice, fun game to play, something one could come back to even after beating the main levels. It was good enough to actually get me to write a review, which is saying something. Other than that tiny control issue, I just can't come up with any other real flaws to nitpick at. Very well done!